1. Field of Invention
The present invention relates to a micro-electro-mechanical system (MEMS) microphone module and a manufacturing process thereof. More particularly, the present invention relates to an MEMS microphone module with an increased back volume and a manufacturing process thereof.
2. Related Art
For integrated circuit element products having microphones, a demand for MEMS microphones is increasing. Recent global mobile phone manufacturers provide an additional microphone for photographing function for practical convenience besides a microphone for communication. Recently, portable audio and digital camera products having micro hard disks or flash memories increasingly features this design so the MEMS microphones may have a considerable market share in the future.
As for the MEMS microphone with thin thickness and small volume, a surface adhesion process can be performed thereon through solder reflow, thereby effectively reducing assembling cost. Therefore, the MEMS microphones are increasingly occupying the original market of electric condenser microphones (ECMs) because of the small volume and low cost. Additionally, the MEMS microphone has an inherent advantage of low power consumption (160 μA), which is approximately ⅓ of that of the ECM. For the mobile phone application with limited power storing capacity, the advantage of power saving also distinctly promotes the MEMS microphone to replace the ECM.
Referring to FIGS. 1A to 1B, in US patent publication No. US 20050185812, a back volume 14 of a microphone package is defined by hollowing downward without penetrating a supporting substrate 11 at a position of the supporting substrate 11 corresponding to a central vibrating thin film 13 of an MEMS microphone chip 12. In addition, a printed circuit board and the supporting substrate are adhered with a hole 15 sandwiched therebetween, and the sandwiched hole 15 region overlaps the hollowed region of the supporting substrate 11, for serving as an extension of the back volume 14 to enlarge the back volume 14. For a common MEMS microphone module design, a size of the common MEMS microphone chip is approximately 2.0 by 2.0 mm, a diameter region of an acoustic wave vibration sensing thin film is approximately 1.0 mm, and the supporting substrate has a thickness of 0.2 to 0.3 mm, so a possible thickness of the sandwiched hollow is approximately 0.07 mm. Generally speaking, in practical compression bonding process of the supporting substrate, it is difficult to control the hollow thickness of the middle layer to be uniform, and the downward extending depth from the diameter region of the acoustic wave vibration sensing thin film is limited by the thickness of the supporting substrate, so the formed space is limited.